#include<iostream>
#include<fstream>
using namespace std ;
int main()
{
	ifstream f("flip.in");
	ofstream g("flip.out");
	int N,M,i,j,a[16][16],s_total=0,s=0;
	f>>N>>M;
	for(i=1;i<=N;i++)
	for(j=1;j<=M;j++)
	f>>a[i][j];
	for(i=1;i<=N;i++)
	{
		s=0;
	
		for(j=1;j<=M;j++)
		{
			s=s+a[i][j];
		}
		if(s<0)
		{
			s=0;
			for(j=1;j<=M;j++)
			{
				if(a[i][j]<0)
				a[i][j]=-a[i][j];
				s=s+a[i][j];
			}
		}
		s_total=s_total+s;}
		g<<s_total;
		return 0;

}